Rationale behind using Imipramine for panic disorder:
Based on literature review: among TCAs, Imipramine have >10 RCT showing efficacy for panic disorder followed by Clomipramine (with 5 RCTs).
Interesting clinical fact from one study is: the effects of imipramine were significantly superior to those of placebo in patients with spontaneous panic attacks, ie, patients with agoraphobia or mixed phobia. In patients with simple phobia, who do not experience spontaneous panic, there was not a significant difference between imipramine and placebo.
Zitrin CM, Klein DF, Woerner MG, Ross DC. Treatment of phobias. I. Comparison of imipramine hydrochloride and placebo. Arch Gen Psychiatry. 1983 Feb;40(2):125-38. (pubmed)
Mavissakalian MR, Perel JM. Long-term maintenance and discontinuation of imipramine therapy in panic disorder with agoraphobia. Arch Gen Psychiatry. 1999 Sep;56(9):821-7. (pubmed)